1. Technical Field
The present invention relates to wireless communications and, more particularly, to a method for phase and frequency shifting an ingoing RF signal.
2. Related Art
Communication systems are known to support wireless and wire lined communications between wireless and/or wire lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, wireless communication systems may operate in accordance with one or more standards, including, but not limited to, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), and/or variations thereof.
Depending on the type of wireless communication system, a wireless communication device, such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, etc., communicates directly or indirectly with other wireless communication devices. For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel or channels (e.g., one of a plurality of radio frequency (RF) carriers of the wireless communication system) and communicate over that channel(s). For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel. To complete a communication connection between the wireless communication devices, the associated base stations and/or associated access points communicate with each other directly, via a system controller, via a public switched telephone network (PSTN), via the Internet, and/or via some other wide area network.
Each wireless communication device includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). As is known, the transmitter includes a data modulation stage, one or more intermediate frequency stages, and a power amplifier stage. The data modulation stage converts raw data into baseband signals in accordance with the particular wireless communication standard. The one or more intermediate frequency stages mix the baseband signals with one or more local oscillations to produce RF signals. The power amplifier stage amplifies the RF signals prior to transmission via an antenna.
Typically, the data modulation stage is implemented on a baseband processor chip, while the intermediate frequency (IF) stages and power amplifier stage are implemented on a separate radio processor chip. Historically, radio integrated circuits have been designed using bipolar circuitry, allowing for large signal swings and linear transmitter component behavior. Therefore, many legacy baseband processors employ analog interfaces that communicate analog signals to and from the radio processor.
Multiple antenna systems are known to be an efficient solution to increase data rate and/or increase robustness by taking advantage of multi-path scattering present in most indoor and urban environments. Phase shifters (PS) are used to set the phase of the received signal from each antenna. These radio frequency (RF) phase shifters have to meet certain requirements, such as having adjustable phase with the range of 360 degrees, having low loss and control complexity, consuming low power, and/or being compact and low cost to be able to be used in commercial applications. As such, it is desirable to provide a phase shifter (e.g., an RF phase shifter) that has a high shift range, a small size, a low cost, and/or a low power consumption. Further, it is desirable to provide a phase and frequency shift circuit that eliminates circuit parts, decreases noise and, more generally, operates in a more desirable manner.
Additionally, mixer circuits, such as the Gilbert Cell mixer, are often used to frequency shift a signal to up-convert or to down-convert a signal from a first to a second frequency. In a typical Gilbert Cell topology, an input signal is applied to a gate of an input MOSFET for mixing with a local oscillation that is applied to a gate of a second input of the mixer circuit. With such a configuration, a gate-to-source voltage drop is experienced at each device receiving an input voltage signal. In today's integrated circuit transceivers, however, low voltages are used as a supply thereby leaving little head room for voltage drops throughout a circuit path. As such, providing phase shifting, mixing and amplification is desirably done in a manner that minimizes voltage drops to leave a maximum amount of head room for signal processing. Along the same lines, FIG. 1 illustrates a prior art amplifier stage that amplifies voltage signals. Generally, a signal source produces an output signal that is converted to a voltage signal by output resistors RL. A voltage signal input is then produced to a buffer that isolates any resistance and output loading at the output of the signal source. As such, the gain of the amplifier stage of FIG. 1 is given by R2/R1, as is known by one of average skill in the art. The output of the amplifier stage is, therefore, an amplified voltage signal. While the circuit of FIG. 1 is operable to amplify a voltage signal, there are specific applications where it is desirable to minimize noise introduced by a circuit or to increase head room to provide greater amplification and better linearity of alternating current signals within the overall circuit.